Active Lava Flows Research Articles

Charting thermal emission variability at Amirani with the Galileo NIMS Io Thermal Emission Database (NITED)

We have examined the variability of thermal emission from lava flows at Amirani on Io, using measurements of radiant flux from detections by the Galileo Near Infrared Mapping Spectrometer (NIMS) between 1996 and 2001. Amirani is the longest currently active lava flow field in the Solar System and a persistent thermal source in every Galileo NIMS observation that covers its location. We have quantified the thermal emission from hot spots correlated with discrete areas of new lava flow emplacement at points along the length of the Amirani flow field in high spatial resolution NIMS observations in 2000 and 2001. Where discernible, the position of some effusive activity changes from orbit to orbit. We find the implied style of emplacement of lava at Amirani is consistent with pahoehoe-like flows. There is an estimated 50% decrease in discharge rate between 1997 and late 2001, perhaps linked to an outburst eruption in the Amirani vicinity in February 2001. The variability of thermal emission from Amirani is less than that seen at a number of other persistently active ionian volcanoes (such as Prometheus, Culann, and Loki Patera). All of these volcanoes exhibit large increases and decreases in the absolute magnitude of thermal emission (see Matson et al., 2006 [Loki Patera]; Davies, A.G. et al. [2006]. Icarus 184, 460–477 [Prometheus]; and Davies, A.G., Ennis, M.E. [2011]. Icarus 215, 401–416 [Culann]). At Amirani, as at these volcanoes, the thermal emission measured between 1996 and 2001 indicates a persistent, although variable, supply of magma to the surface. In high spatial resolution NIMS observations of hot spots obtained in 2000 and 2001 we estimate the emitted power from active lava flows associated with Amirani to be ∼170±30GW, which corresponds to total effusion rates (assuming a basaltic composition) from multiple points along the Amirani flow of 34–56m3/s.

A field investigation of the basaltic ring structures of the Channeled Scabland and the relevance to Mars

The basaltic ring structure (BRS) is a class of peculiar features only reported in the Channeled Scabland of eastern Washington State. They have been suggested to be good analogs, however, for some circular features on Mars. BRSs are found where Pleistocene floods scoured the Columbia River Basin, stripping off the uppermost part of the Miocene Columbia River Basalt Group and exposing structures that were previously embedded in the lava. The “Odessa Craters,” near Odessa, WA, are 50–500-m-wide BRSs that are comprised of discontinuous, concentric outcrops of subvertically-jointed basalt and autointrusive dikes. Detailed field investigation of the Odessa Craters in planform and a cross-sectional exposure of a similar structure above Banks Lake, WA, lead us to propose that BRSs formed by concurrent phreatovolcanism and lava flow inflation. In this model, phreatovolcanic (a.k.a., “rootless”) cones formed on a relatively thin, active lava flow; the lava flow inflated around the cones, locally inverting topography; tensile stresses caused concentric fracturing of the lava crust; lava from within the molten interior of the flow exploited the fractures and buried the phreatovolcanic cones; and subsequent erosive floods excavated the structures. Another population of BRSs near Tokio Station, WA, consists of single-ringed, raised-rimmed structures that are smaller and more randomly distributed than the Odessa Craters. We find evidence for a phreatovolcanic component to the origin as well, and hypothesize that they are either flood-eroded phreatovolcanic cones or Odessa Crater-like BRSs. This work indicates that BRSs are not good analogs to the features on Mars because the martian features are found on the uneroded surfaces. Despite this, the now superseded concepts for BRS formation are useful for understanding the formation of the martian features.

Time‐averaged discharge rate of subaerial lava at Kīlauea Volcano, Hawai‘i, measured from TanDEM‐X interferometry: Implications for magma supply and storage during 2011–2013

AbstractDifferencing digital elevation models (DEMs) derived from TerraSAR add‐on for Digital Elevation Measurements (TanDEM‐X) synthetic aperture radar imagery provides a measurement of elevation change over time. On the East Rift Zone (EZR) of Kīlauea Volcano, Hawai‘i, the effusion of lava causes changes in topography. When these elevation changes are summed over the area of an active lava flow, it is possible to quantify the volume of lava emplaced at the surface during the time spanned by the TanDEM‐X data—a parameter that can be difficult to measure across the entirety of an ~100 km2 lava flow field using ground‐based techniques or optical remote sensing data. Based on the differences between multiple TanDEM‐X‐derived DEMs collected days to weeks apart, the mean dense‐rock equivalent time‐averaged discharge rate of lava at Kīlauea between mid‐2011 and mid‐2013 was approximately 2 m3/s, which is about half the long‐term average rate over the course of Kīlauea's 1983–present ERZ eruption. This result implies that there was an increase in the proportion of lava stored versus erupted, a decrease in the rate of magma supply to the volcano, or some combination of both during this time period. In addition to constraining the time‐averaged discharge rate of lava and the rates of magma supply and storage, topographic change maps derived from space‐based TanDEM‐X data provide insights into the four‐dimensional evolution of Kīlauea's ERZ lava flow field. TanDEM‐X data are a valuable complement to other space‐, air‐, and ground‐based observations of eruptive activity at Kīlauea and offer great promise at locations around the world for aiding with monitoring not just volcanic eruptions but any hazardous activity that results in surface change, including landslides, floods, earthquakes, and other natural and anthropogenic processes.

The influence of cross-sectional channel geometry on rheology and flux estimates for active lava flows

Lava rheology and effusion rate are critical factors in determining the evolution of lava flows. However, direct and accurate field measurements are difficult to carry out, and estimates are usually based on measurements of the flow’s surface velocity and assumptions of sub-surface geometry. Using numerical flow models, we show that the potential for error due to geometry uncertainty is minimized if a semi-elliptical cross-sectional channel shape is assumed. Flow is simulated for isothermal Newtonian, temperature-dependent Newtonian, and isothermal power-law rheology lavas. For isothermal Newtonian lava, we find that the error in channel shape alone can make apparent viscosity estimates ∼3.5 times too large (e.g., for inappropriate use of the Jeffreys equation on a narrow semi-elliptical channel). For a temperature-dependent rheology, using an analytical approximation for Newtonian flow in a semi-elliptical geometry yields apparent viscosity and flux values that are more accurate than estimates which assume a rectangular geometry, for all channel shapes considered, including rectangular channels. Viscosity calculations for real channels on Mauna Loa and Mount Etna show that for a Newtonian rheology, a semi-elliptical analytical solution gives an approximation three times closer to the actual viscosity than a rectangle with the same depth while, if the lava is shear-thinning (power law exponent m = 0.6), a rectangular approximation is 15 % more accurate. Our results can be used to bracket possible viscosity and flux estimates when channel topography is poorly constrained.

Lava discharge rate estimates from thermal infrared satellite data for Pacaya Volcano during 2004–2010

Pacaya is one of the most active volcanoes in Central America and has produced lava flows frequently since 1961. All effusive activity between 1961 and 2009 was confined by an arcuate collapse scarp surrounding the northern and eastern flanks. However, the recent breaching of this topographic barrier, and the eruption of a large lava flow outside of the main center of activity, have allowed lava to extend into nearby populated areas, indicating the need for assessment and monitoring of lava flow hazards. We investigated whether a commonly used satellite-based model could produce accurate lava discharge rates for the purpose of near-real-time assessment of hazards during future eruptions and to assess the dynamics of this persistently degassing system. The model assumes a linear relationship between active lava flow area and time-averaged discharge rate (TADR) via a simple conversion factor. We calculated the conversion factor via two methods: (1) best-fitting of satellite-derived flow areas to ground-based estimates of lava flow volume, and (2) theoretically via a parameterized model that takes into account the physical properties of the lava. To apply the latter method, we sampled four lava flows and measured density, vesicularity, crystal content, and major element composition. We found the best agreement of conversion factors in the eruption with the most complete satellite coverage, and used data for these flows to define the linear relationship between area and discharge rate. The physical properties of the sampled flows were essentially identical, so that any discrepancy between the two methods of calculating conversion factors must be due to modeling errors or environmental factors unaccounted for by the parameterized model. However, our best-fitting method provides a new means to set the conversion appropriately, and to obtain self-consistent TADRs. We identified two distinct types of effusive activity at Pacaya: Type 1 activity characterized by initially high TADRs of about 1–10m3·s−1, followed by a waning phase, and Type 2 activity characterized by low, scattered TADRs of about 0.1–1m3·s−1. The risk associated with Type 1 activity is much higher, so identifying the Type 1 radiance signature in satellite imagery is useful for monitoring an ongoing eruption.

Rheological control on the radiant density of active lava flows and domes

During an effusive–extrusive eruption, the capability of an active lava body (flow or dome) to radiate thermal energy depends on how the lava discharge rate is accommodated by the expansion of the magma body and by the cooling of its surface. This feature can be described by a single empirical parameter, defined “radiant density” (crad; in Jm−3) that, for a given discharge rate, expresses the efficiency of the lava body to change its area and/or to insulate its inner core, thus modulating the heat radiated from the active surface. By comparing the Volcanic Radiative Energy (VRE; in J), detected by MODIS during 28 eruptions at 18 active volcanoes, with their erupted lava volumes (Vol; in m3), we show that the radiant density (crad=VRE/Vol) is inversely proportional to the silica content of the erupted lava. Basic lavas (45–52wt.% SiO2) have the highest observed radiant density (1 to 4×108Jm−3) while intermediate (52–63wt.% SiO2) and acidic (>63wt.% SiO2) lavas show a gradually lower radiant densities (1.5 to 9×107Jm−3 and 0.2 to 1×107Jm−3 for intermediate and acidic composition, respectively). We regard this correlation as the result of the control that the rheology of lavas exerts on cooling and spreading processes of related bodies. In particular, we found that for any given compositional group the radiant density is essentially related to a “characteristic thickness” of active lavas, at the time of a satellite acquisition.We suggest that the radiant density of effusive/extrusive lava bodies can be predicted (±50%) by means of an empirical relationship based on the SiO2 content of the erupted lava. This makes this parameter very useful in observing volcanic activity, especially in remote regions where access may not be possible. By measuring the energy radiated during an eruption and by assuming a lava composition (based on the tectonic setting or magmatic province), we suggest that the radiant density can be used to estimate lava discharge rates and erupted volumes for volcanoes characterised by effusive or extrusive activity.

Morphometric analysis of lava flow units: Case study over LIDAR-derived topography at Mount Etna, Italy

High resolution, LIDAR-derived digital elevation models of volcanic areas can significantly improve knowledge of lava flow morphology and emplacement mechanisms. Here we focus on single flow units, presenting a new semi-automatic procedure which provides a quantitative analysis of their shape. The method relies on the automatic processing of the elevation profiles obtained on transects orthogonal to the flow unit axis. The initial phase of the Mount Etna flank eruption from September 2004 is taken as test case, and the procedure is applied on an active lava flow, which was emplaced on the eastern flank of the volcano. The main topographic dataset used is a 2-m-resolution digital elevation model obtained from a LIDAR survey. Starting from the axis of a lava flow unit, our method yields morphometric data on the flow unit at a 2m spacing, calculating parameters including flow width, channel width, the heights of the levees, inward and outward slope of levees, and estimating pre-emplacement slope along the axis. The procedure is embedded in a customized GIS, which allows easy processing, handling and displaying of data. The procedure has also been applied to another flow unit emplaced during the October–November 1999 overflow from the Bocca Nuova crater. Results show that the channel width seems to accommodate first‐order trends of the pre-emplacement slope along the flow unit axis, while it is little affected by high frequency changes in slope; in contrast, flow unit width and flow unit thickness are apparently influenced by small‐scale changes in slope. The different emplacement conditions of the two flow units are reflected by the overall contrasting morphologies, as shown by the different average thickness and by the different ratios between (i) flow width vs. channel width and (ii) flow unit section area vs. channel width. The new method provides an enhanced, systematic and thorough morphometric description of flow units, which may improve the understanding of the emplacement mechanisms of lava flows on Earth and other planets.

Tracking lava flow emplacement on the east rift zone of Kīlauea, Hawai‘i, with synthetic aperture radar coherence

Lava flow mapping is both an essential component of volcano monitoring and a valuable tool for investigating lava flow behavior. Although maps are traditionally created through field surveys, remote sensing allows an extraordinary view of active lava flows while avoiding the difficulties of mapping on location. Synthetic aperture radar (SAR) imagery, in particular, can detect changes in a flow field by comparing two images collected at different times with SAR coherence. New lava flows radically alter the scattering properties of the surface, making the radar signal decorrelated in SAR coherence images. We describe a new technique, SAR Coherence Mapping (SCM), to map lava flows automatically from coherence images independent of look angle or satellite path. We use this approach to map lava flow emplacement during the Pu‘u ‘Ō‘ō‐Kupaianaha eruption at Kīlauea, Hawai‘i. The resulting flow maps correspond well with field mapping and better resolve the internal structure of surface flows, as well as the locations of active flow paths. However, the SCM technique is only moderately successful at mapping flows that enter vegetation, which is also often decorrelated between successive SAR images. Along with measurements of planform morphology, we are able to show that the length of time a flow stays decorrelated after initial emplacement is linearly related to the flow thickness. Finally, we use interferograms obtained after flow surfaces become correlated to show that persistent decorrelation is caused by post‐emplacement flow subsidence.

Tumulus development on lava flows: insights from observations of active tumuli and analysis of formation models

Here, we use observations of active flows along with detailed morphometric field measurements of more than 70 tumuli on flows at Mount Etna (Italy), Kilauea, and Hualalai (US) volcanoes to constrain a previously published model that estimates the pressure needed to form tumuli. In an attempt to discover the nature and magnitude of pressure variations within active lava flow interiors, we then consider how tumuli differ from idealized circular plates. We incorporate observations of active tumuli and find that they may grow asymmetrically yet produce a symmetrical tumulus and can form where the flow path significantly changes direction. Bending models of clamped edges provide the most reasonable head estimates for the tumuli in our study. Tumulus formation requires the proper combination of cooling and effusion rate. If cooling is too extensive and effusion rate too low, the crust will provide too much resistance to bending. If cooling is too limited and effusion rates too high, crusts will not develop or have insufficient strength to resist fracture and subsequent breakouts. We do not find it surprising that tumuli are rarely found over well-established lava tubes that typically have rigid, walls/overlying crusts that exceed 2 m in thickness and provide too much resistance to bending. Silicic flows lack tumuli because the viscosity gradients within the flow are insufficient to concentrate stress in a localized area.

Near real-time routine for volcano monitoring using infrared satellite data

An Advanced Very-High-Resolution Radiometer (AVHRR) routine for hotspot detection and effusion rate estimation (AVHotRR) using AVHRR infrared space-borne images is presented here for the monitoring of active lava flow. AVHotRR uses directly broadcast National Oceanic and Atmospheric Administration (NOAA)-AVHRR remotely sensed data. The 2006 summit eruption of Mount Etna provided the opportunity to test the products generated by AVHotRR for monitoring purposes. Low spatial and high temporal resolution products can also be used as inputs of flow models to drive numerical simulations of lava-flow paths and thus to provide quantitative hazard assessment and volcanic risk mitigation.

Speculations about the Effects of Fire and Lava Flows on Human Evolution

Recent research argues that an association with fire, stretching back millions of years, played a central role in human evolution resulting in many modern human adaptations. Others argue that hominin evolution was driven by the roughness of topographic features that resulted from tectonic activity in the African Rift valley. I combine these hypotheses to propose that, for millions of years, active lava flows in the African Rift provided consistent but isolated sources of fire, providing very specific adaptive pressures and opportunities to small isolated groups of hominins. This allowed these groups of early hominins to develop many fire specific adaptations such as bipedalism, smaller teeth and mouths, shorter intestines, larger brains, and perhaps a host of social adaptations. By about 1.8 million years ago, Homo erectus emerged as a fire adapted species and mastered the technology necessary to make fire itself. This technology allowed them to move into the rest of the world, taking a new kind of fire with them that would change ecosystems everywhere they went. This hypothesis is supported by recent geologic work that describes a large lava flow occurring in the region of the Olduvai Gorge during the 200 000 year time period we believe Homo erectus emerged in the area.

Generation of pyroclastic flows by explosive interaction of lava flows with ice/water-saturated substrate

We describe a new type of secondary rootless phreatomagmatic explosions observed at active lava flows at volcanoes Klyuchevskoy (Russia) and Etna (Italy). The explosions occurred at considerable (up to 5 km) distances from primary volcanic vents, generally at steep (15–35°) slopes, and in places where incandescent basaltic or basaltic-andesitic lava propagated over ice/water-saturated substrate. The explosions produced high (up to 7 km) vertical ash/steam-laden clouds as well as pyroclastic flows that traveled up to 2 km downslope. Individual lobes of the pyroclastic flow deposits were up to 2 m thick, had steep lateral margins, and were composed of angular to subrounded bomb-size clasts in a poorly sorted ash–lapilli matrix. Character of the juvenile rock clasts in the pyroclastic flows (poorly vesiculated with chilled and fractured cauliflower outer surfaces) indicated their origin by explosive fragmentation of lava due to contact with external water. Non-juvenile rocks derived from the substrate of the lava flows comprised up to 75% in some of the pyroclastic flow deposits. We suggest a model where gradual heating of a water-saturated substrate under the advancing lava flow elevates pore pressure and thus reduces basal friction (in the case of frozen substrate water is initially formed by thawing of the substrate along the contact with lava). On steep slope this leads to gravitational instability and sliding of a part of the active lava flow and water-saturated substrate. The sliding lava and substrate disintegrate and intermix, triggering explosive “fuel–coolant” type interaction that produces large volume of fine-grained clastic material. Relatively cold steam-laden cloud of the phreatomagmatic explosion has limited capacity to transport upward the produced clastic material, thus part of it descends downslope in the form of pyroclastic flow. Similar explosive events were described for active lava flows of Llaima (Chile), Pavlof (Alaska), and Hekla (Iceland) indicating that this type of explosions and related hazard is common at snow/ice-clad volcanoes and sometimes happens also on fluid-saturated hydrothermally altered slopes.

Evolution of an active lava flow field using a multitemporal LIDAR acquisition

Application of light detection and ranging (LIDAR) technology in volcanology has developed rapidly over the past few years, being extremely useful for the generation of high‐spatial‐resolution digital elevation models and for mapping eruption products. However, LIDAR can also be used to yield detailed information about the dynamics of lava movement, emplacement processes occuring across an active lava flow field, and the volumes involved. Here we present the results of a multitemporal airborne LIDAR survey flown to acquire data for an active flow field separated by time intervals ranging from 15 min to 25 h. Overflights were carried out over 2 d during the 2006 eruption of Mt. Etna, Italy, coincident with lava emission from three ephemeral vent zones to feed lava flow in six channels. In total 53 LIDAR images were collected, allowing us to track the volumetric evolution of the entire flow field with temporal resolutions as low as ∼15 min and at a spatial resolution of <1 m. This, together with accurate correction for systematic errors, finely tuned DEM‐to‐DEM coregistration and an accurate residual error assessment, permitted the quantification of the volumetric changes occuring across the flow field. We record a characteristic flow emplacement mode, whereby flow front advance and channel construction is fed by a series of volume pulses from the master vent. Volume pulses have a characteristic morphology represented by a wave that moves down the channel modifying existing channel‐levee constructs across the proximal‐medial zone and building new ones in the distal zone. Our high‐resolution multitemporal LIDAR‐derived DEMs allow calculation of the time‐averaged discharge rates associated with such a pulsed flow emplacement regime, with errors under 1% for daily averaged values.

Cooling rate of some active lavas determined using an orbital imaging spectrometer

The surface temperature of an active lava flow is an important physical property to measure. Through its influence on lava crystallinity, cooling exerts a fundamental control on lava rheology. Remotely sensed thermal radiance data acquired by multispectral sensors such as Landsat Thematic Mapper and the Terra Advanced Spaceborne Thermal Emission and Reflection Radiometer are of insufficient spectral and radiometric fidelity to allow for realistic determination of lava surface temperatures from Earth orbit. This paper presents results obtained from the analysis of active lava flows using hyperspectral data acquired by NASA's Earth Observing‐1 Hyperion imaging spectrometer. The contiguous nature of the measured radiance spectrum in the 0.4–2.5 μm region means that, although sensor saturation most certainly occurs, unsaturated radiance data are always available from even the hottest, and most radiant, active lava flow surfaces. The increased number of wave bands available allows for the assumption of more complex flow surface temperature distributions in the radiance‐to‐temperature inversion processes. The technique is illustrated by using a hyperspectral image of the active lava lake at Erta Ale volcano, Ethiopia, a well‐characterized calibration target, a time series of three Hyperion images of an active lava flow acquired during a 4 day period at Mount Etna, Sicily, as well as a lava flow erupted at Nyamuragira, Democratic Republic of Congo. The results provide insights into the temperature–radiance mixture modeling problem that will aid in the analysis of data acquired by future hyperspectral remote sensing missions, such as NASA's proposed HyspIRI mission.

Imaging short period variations in lava flux

Short period (e.g. <1 h) variations in lava effusion rate have been detected previously on Mount Etna, Sicily, but the causes and effects of such changes are poorly understood because of difficulties in obtaining suitably high frequency measurements over long periods. Here, we report short period flux variations in active lava flows, recorded in dense time series imagery over a 7-night period using modified remote trail cameras. The sequences of night-time images show significant pulses of enhanced incandescence, interpreted as short period increases in lava flux, travelling down-channel at velocities of ∼10–20 m min−1. Pulse generation decreased from an average of one pulse per hour on the first night to approximately one per night within a few nights. Effusion rate changes on these timescales are considered to reflect instabilities in magma ascent and, consequently, could provide insight into subsurface flow processes.

Wavelength influence in sub-pixel temperature retrieval using the dual-band technique

The thermal model proposed by Crisp and Baloga (1990) for active lava flows considers thermal flux as a func- tion of the fractional area of two thermally distinct radiant surfaces. In this model, the larger surface area corre- sponds to the cooler crust of the flow and the other, much smaller to fractures in the crust. These cracks temper- ature is much higher than the crust one and approaches the temperature of the molten or plastic interior flow. The dual-band method needs two distinct SWIR (short wave infrared) bands to formulate a two equations sys- tem from the simultaneous solution of the Planck equation in each band. The system solutions consist in the crust temperature and the fractional area of the hot component. The dual band technique originally builds on data ac- quired by sensors (such as Landsat TM) with two SWIR bands only. The use of hyperspectral imaging spectrom- eters allows us to test the dual-band technique using different wavelengths in the SWIR range of the spectrum. DAIS 7915 is equipped with 40 bands into the range 1.54-2.49 nm which represent potential input in dual band calculation. This study aims to compare results derived by inserting assorted couples of wavelengths into the equation system. The analysis of these data provides useful information on dual-band technique accuracy.

Detecting the development of active lava flow fields with a very‐long‐range terrestrial laser scanner and thermal imagery

Regular topographic surveys of active lava flows could provide significant insight into the development of flow fields, but data of sufficient accuracy, spatial extent and repeat frequency to quantify the processes involved have yet to be acquired. Here, we report results from the use of a new very‐long‐range terrestrial laser scanner (TLS) on active lavas at Mount Etna, Sicily. The scanner proved capable of providing useful topographic data from volcanic terrain at ranges up to ∼3500 m, with laser returns from ash‐covered slopes as well as from lava. Despite very low effusion rates (&lt;1 m3s−1), topographic changes associated with the emplacement and inflation of new flows and the inflation of a tumulus were detected. Irregular data spacing resulting from oblique views makes the interpretation of laser‐derived digital elevation models alone difficult, but fusing topographic data with thermal images allows active flow features to be clearly visualized.

Combined Use of SEVIRI and MODIS for Detecting, Measuring, and Monitoring Active Lava Flows at Erupting Volcanoes

Multispectral data acquired by Spinning Enhanced Visible and InfraRed Imager (SEVIRI) onboard the geostationary platform Meteosat Second Generation (MSG2), located at 0deg longitude, were analyzed to assess the payload suitability for quantitative volcano monitoring. In times of good infrared transparency of the troposphere, SEVIRI data proved particularly suited to detect the onset of effusive eruptions and to monitor the related lava flows with 15-min refresh rates. After development of a code allowing for fast automated processing of the 96 data streams downlinked daily by MSG2, thorough monitoring tests were carried out on the 2007 eruptions of Stromboli (Aeolian Islands, Italy) and Piton de la Fournaise (Reunion Island, France). The results in radiant flux and effusion rate provided by use of thermal, mid-, and short infrared bands of SEVIRI were validated by exploiting simultaneous MODIS overpasses by Terra and Aqua, up to four times daily.

Assumptions in the evaluation of lava effusion rates from heat radiation

The availability of high‐resolution thermal imagery of active lava flows has stimulated the use of radiance maps for the evaluation of lava effusion rates. This is made possible by simple formulae relating the lava flow rate to the energy radiated per unit time from the planimetric surface of the flow. Such formulae are based on a specific flow model and, consequently, their validity is subject to the model assumptions. An analysis of these assumptions reveals that the current use of the formulae is not consistent with the model. The reason why they provide reasonable, although very rough, values for effusion rates appears to be that the actual radiated energy is controlled by a feature (the nonuniform temperature of flow surface) which is not accounted for by the model and which counterbalances the effect of inconsistent use of the formulae.

Using infrared satellite data to drive a thermo‐rheological/stochastic lava flow emplacement model: A method for near‐real‐time volcanic hazard assessment

We combine two flow simulation models to provide a computationally efficient means of predicting the final dimensions of active lava flows. By using a stochastic approach to predict all the downhill paths that a lava flow could possibly follow and a thermo–rheological model to terminate these paths once the predicted cooling–limited length for the flow has been attained, this approach allows for rapid assessment of the area likely to be inundated by lava. The 1991–1993 eruption of Mount Etna is used as a case study. Lava effusion rate exerts a strong control on the maximum length a lava flow can attain, and we demonstrate how the model can be driven by time–varying effusion rates, obtained from infrared satellite data. As such data are obtained in near–real–time, this approach allows flow simulations to be updated in a timely manner, in response to changing eruption conditions.